This invention relates to monitoring the operation of a heating or cooling system, and more specifically to monitoring the level of refrigerant charge present in the refrigeration circuit of any such system.
Many heating and/or cooling systems employ refrigeration circuits. Heat pumps, for instance, use a refrigeration circuit to absorb heat from beneath the ground that can be thereafter surrendered through a heat exchanger to air in a building that is to be heated by the heat pump. Chiller systems on the other hand absorb heat from water flowing through an evaporator so as to thereby chill the water. The chilled water is ultimately used to cool the air in a building by virtue of the chilled water absorbing heat from the air flowing through a heat exchanger. It is important that both the heat pump and the chiller have a sufficient or adequate charge of refrigerant in order to accomplish their respective functions.
It is also important to detect any change in refrigerant charge before the heating or cooling system has operated at an undercharged or overcharged condition for a prolonged period of time. In this regard such changes, if significant, could cause harm to the system. Any such change in refrigerant charge may also be potentially harmful to the atmosphere in the event that the change is attributable to a refrigerant leakage.
Heating or cooling systems have heretofore been equipped with a variety of alarms that may detect an inadequate refrigerant charge. For instance a chiller system equipped with alarms located primarily at the inlet side of one or more of the system's compressors may be triggered due to low refrigerant charge. These alarms may however also be triggered due to other problems occurring within the system. For example, alarms for monitoring suction pressure or suction temperature at the inlet of the compressor may also be triggered due to a stuck expansion valve or fan failure. These alarms may also not be triggered until a substantial amount of refrigerant has been lost. This would occur if the thresholds for the alarms were improperly set. For example, the alarms for monitoring suction pressure or suction temperature at the inlet of the compressor may be set too low.
It is to be noted that certain attempts have been made to define a variable limit for triggering the alarm of a particularly monitored refrigerant condition. For instance, the limit for the refrigerant pressure in the condenser unit in a chiller is varied for a particular load conditions in U.S. Pat. No. 5,539,385. This is, however, a varied limit for only a particular condition as opposed to monitoring a combination of conditions present within the chiller system.
It is an object of the invention to detect early loss of small amounts of refrigerant without reliance on individual thresholds of one or more alarms being exceeded.
It is another object of the invention to detect incremental changes in refrigerant charge without relying on one or more alarms that may be triggered for a variety of possible reasons.